"What actually is Zone 2?" is being asked everywhere at the moment. Podcasts, Instagram, your mate at the club who now refuses to run at anything except a shuffle.
It has become one of those terms that sounds far more complicated than it is, so let's strip it back.
BLUF: Zone 2 is easy, conversational aerobic work. Most people should do a lot of it, and most people do it far too hard.
Where the noise came from
This is not a new idea. Endurance coaches have been building athletes on easy aerobic volume for decades. What changed is the audience. Searches for Zone 2 training rose by more than 850% between 2020 and 2023, largely off the back of podcasts featuring sports scientists talking about mitochondria and longevity.
So the science is sound. The problem is that a lot of people picked up the label without the substance.
What Zone 2 actually is
In plain terms: an effort you could hold for a long time, while still holding a conversation. Not gasping. Not chatting away like you are on a walk either. Comfortable, controlled, slightly boring.
In numbers, it usually sits around 60 to 70% of your maximum heart rate, or roughly RPE 3 to 4 out of 10.
The physiological point is that this intensity develops your aerobic engine: your body gets better at using oxygen and burning fat for fuel, without the fatigue cost of hard sessions. That way, we can accumulate a lot of it week after week without breaking you.
Why slower makes you faster
Here is the part that feels counter-intuitive.
Your race, whether that is a 70.3, a marathon or a Hyrox, is mostly an aerobic event. The bigger your aerobic base, the faster you can go while still being comfortable, and the less damage each hard session does to you.
So, what that means is: easy days build the engine, hard days sharpen it. If every session sits in the middle, you get tired without getting fitter. That grey zone is where a lot of frustrated athletes live.
For example: two runners both training 5 hours a week. One runs everything at a moderate slog. The other runs 4 hours easy and 1 hour genuinely hard. Twelve weeks later, the second runner is faster, fresher and still healthy.
The mistakes I see most
- Running their “Zone 2” run at Zone 3 pace. If you cannot speak in full sentences, you are not in Zone 2. Ego is the main obstacle here, not fitness.
- Using zones built on a bad max heart rate. The old "220 minus age" formula carries an error of roughly plus or minus 10 to 12 beats, and every zone built on it inherits that error.
- Chasing heart rate on a hot day. Heat, poor sleep, caffeine and stress all push heart rate up. On those days your watch will tell you to slow down when the effort is honestly fine.
- Doing nothing but Zone 2. You still need hard work. Zone 2 is the base of the pyramid, not the whole pyramid.
How to find yours without a lab
Here's what to do:
- Use the talk test first. It is free, it is instant and it accounts for how you actually feel today. If you can hold a conversation but would rather not sing, you are about right.
- Back it up with numbers. Work out your zones with our Heart Rate Zones calculator, using a real max heart rate from a hard session rather than a formula if you have one.
- Anchor it to effort. Our guide to RPE explains how a felt 1 to 10 number maps onto pace, power and heart rate, and why effort is often the more reliable guide of the two.
- Give it eight weeks. Aerobic adaptation is slow and quiet. You will notice it first as the same pace at a lower heart rate.
How much of it?
A reasonable rule for most people balancing training with a full life: roughly 70 to 80% of your weekly training at genuinely easy effort, with the rest hard and purposeful. One full rest day a week.
That being said, if you only have four hours a week, the split matters less than the consistency. Get the hours in, keep most of them easy, and let the plan grow with you.
The bottom line
Zone 2 is not a hack and it is not a trend. It is the boring, repeatable work that makes everything else possible.
The key message here is: slow down enough that you can keep coming back tomorrow. Better to be consistently good, than sporadically great.
If you are not sure whether your easy days are actually easy, don't sit on it, let me know.